The present invention relates to a top feed device for a sewing machine having an upper feed dog actuatable in synchronism with a lower feed dog for composite movement composed of horizontal motion and vertical motion.
Prior top feed devices for sewing machines have an upper feed dog disposed on a free end of an upper feed arm journalled for vertical angular movement on a drive member which is operatively connected to a lower feed dog and reciprocally movable in a horizontal direction. The upper feed dog can vertically be moved by a spring for depressing the upper feed arm and a crank swingable vertically in coaction with a main shaft. More specifically, the upper feed arm is raised against the action of the spring when the crank is angularly moved upwardly, and is lowered with the crank under the force of the spring when the crank is angularly moved downwardly. After the upper feed dog movable up and down with the swinging movement of the crank has been lowered to reach a fabric on the throat plate, the upper feed dog will not be lowered anymore and will not follow the downward swinging movement of the crank, but instead will feed the fabric while being pressed thereagainst under the bias of the spring. During the fabric feeding movement, the crank continues to swing down to a lower limit and then up toward an upper limit. On the upward swinging movement, the crank engages and lifts the upper feed arm, thus raising the upper feed dog clear of engagement with the fabric. When the crank hits the upper feed arm, there is produced an impact sound, which sound increases in volume as the speed of operation of the sewing machine increases.
There has been proposed an attempt for dampening such an impact by providing a damper between the upper feed arm and the crank.